1 character that has not completed andariel quest/moved to act2. It can simply be a newly created character. ('Game maker')1 character with access to act2 holding the stuff you want to copy ('Mule')1 character with access to act2 that will trade with the mule ('Trader')

Now onto the duping...

Game maker opens a game, Mule and Trader joins.Game maker can now leave.

Mule blocks sent 0x30 and interacts with jerhyn then moves to the waypoint where Trader is waiting.Mule sends the take wp packet: 49 xx xx xx xx 00 00 00 00 where xx = wp id.

Mule and Trader enters trade.Mule receives 77 0C and runs out of town. When you run out of town, Jerhyn that you previously interacted with will get moved to the palace and this cancels the trade on your side, but it's still open for Trader.

Voilá, you can now go act1 with the mule and drop all your loot and come pick it up with another character.

When you're done, simply cancel trade from Trader to rollback the items on Mule.

Start one Diablo II client that you will use as your Mule and run loader.exe, it will inject Dupes.dll into the first Game.exe it finds so it's important you only have one running (or use another better loader)Now start your other clients.

Once ingame, with Dupes.dll loaded on the Mule character:

Press F9 -> Talk to Jerhyn -> Click on Waypoint -> Enter trade with Trader that should be waiting on act2 wp -> Press F9 -> Run out of town -> Now Go Act1 and do your thing! I even put together a video showing how it's done: https://www.youtube.com/watch?v=r_k4BZl_11Y